Magnetoresistive sensors, such as giant magnetoresistive (GMR), are often used in angle sensing applications. A drawback of these sensors, however, is that while they can detect the direction of a magnetic field they are not sensitive to the amplitude of the magnetic field. In some applications this is of no consequence, but in others, such as automotive, relevant safety standards require a minimum magnetic field to ensure angle accuracy. This can be important because angle error generally increases at low magnetic fields, as depicted in FIG. 1. In FIG. 1, it can be seen that if the magnetic field strength falls below about 20 mT, the angle error increases significantly. Therefore, a reduction or loss of magnetic field during operation must be detected in certain safety-related applications.
Conventional approaches include use of vertical Hall devices for angle sensing instead of GMR devices, or combining a GMR sensor for direction sensing with a Hall sensor for amplitude sensing. Vertical Hall devices, however, are not as sensitive as GMR devices, while the addition of a lateral Hall device requires additional space that may be at a premium or not available at all.
Therefore, there is a need for improved xMR angle sensors.